We are conducting an interdisciplinary investigation of the enzymes necessary for the hydroxylation of aromatic amino acids in mammals. All useful approaches to the analysis of the large variety of components involved in these and related reactions are in progress to help elucidate the basic molecular interactions in normal and diseased individuals. We have recently added tyrosine hydroxylase to the cDNAs that we have cloned and expressed to facilitate the study of mechanisms of these enzymes. We have also increased our activities in site directed mutagenesis with, for example, modifications of a number of putative functional sites in phenylalanine hydroxylase to understand the structure-function relationships in these systems.